The present invention relates generally to an improved flame retardant composition, and more particularly to a flame retardant formulation which is particularly adapted to be applied in aqueous working dispersion form onto surfaces of normally combustible materials including woods, fabrics of natural fiber, synthetic resin foams and fabrics, steel, and the like. The formulation of the present invention has particular efficacy in flame retardant applications as a result of its ability to create a substantially continuous protective film as it undergoes a transition of composition over a broad range of exposure to flame so as to encapsulate and surface-envelope the article and/or structure onto which it is applied. The film is insulative and excludes oxygen from the substrate. It radiates infrared and visible light at higher temperatures. Films formed with the formulation of the present invention have excellent fire retardant properties, and in addition, as films, are flexible, have excellent adhesion, and provide a coating with outstanding tensile strength.
In the past, various flame and fire retardant compositions have been proposed having particular application as a surface coating for a wide variety of materials. Traditionally, these materials have contained certain active flame or fire retardant ingredients which, in the presence of flame and/or heat, become donors and/or generators of elemental chlorine, bromine, and/or phosphorus. The acidic fire retardants also catalyze conversion of polymeric binders into graphite-like continuous char layers at temperatures below the combustion temperature range. Other formulations included oxides of antimony and the like. In the present formulation, the arrangement is such that donors of chlorine, bromine, and phosphorus are provided for their capability, as well as antimony oxide, together with a quantity of hydrated alumina for its water release capability. The result is a highly effective flame retardant material which functions well and which does not release large quantities of nascent chlorine, bromine, HCl, HBr, HCN, No or ammonia gases. Carbon monoxide and smoke emmisions are controlled to a level which is not hazardous.
Films formed with the formulation of the present invention are highly useful in the encapsulation of asbestos, with the coating having low temperature flexibility, as well as elastomeric properties which contribute to the lifetime of the finished coating. In addition, the materials have good adhesion properties, and because of the physical properties of the aqueous materials being applied, are capable of penetrating and wetting the asbestos fibers. These materials resist combustion at temperatures up to approximately 1000.degree. F. by gradually converting from a polyvinylchloride-acrylic polymer film to a graphitic char film through chemical interaction of the polymer with the acidic fire-retardant chemicals present in the formulation. Additionally, acid gas emissions such as gaseous hydrogen chloride, hydrogen bromide, and hydrogen phosphate are moderated and controlled in part by chemical reaction with the calcium carbonate component. It has been found that at temperatures of between about 1000.degree. F. and 2000.degree. F., a continuous inorganic film is formed which functions as a refractory fire barrier, with the film integrity being maintained by interactions of pigment components of the formulation so as to establish, create, and form a substantially continuous coating with ceramic properties.